A first assessment of polyester-urethane cutin-based coating for the protection of outdoor bronzes.

New and patinated quaternary bronze specimens were coated with an innovative poly(ester-urethane) cutin-based coating. Alongside uncoated specimens, they underwent accelerated ageing to assess the anti-corrosion properties and durability of the coating. The ageing procedure sim- ulated the action of both run-off and stagnant rainwater, as well as temperature, relative humidity and UVA expo- sure conditions typical of southern Europe. Additionally, synthetic particulate matter (PM) containing soluble and insoluble inorganic compounds, as well as elemental carbon, was prepared and deposited on a coated specimen which was then subjected to temperature and relative humidity variations. Specimens were characterized before and after each step of the ageing procedure by UV-Vis spectrophotometry for colour analysis, scanning electron microscopy, infrared and Raman spectroscopy. Synthetic rain solutions that came into contact with the specimens during the ageing process were collected and analysed by microwave-plasma atomic emission spectroscopy for quantification of released metals. Results indicate a good resistance of the coating to the action of rainwater, as metal release from coated specimens is consistently lower than from uncoated specimens. The structure of the coating remains unchanged and the coating layer remains continuous after ageing. Evaluation of the effects of synthetic PM after 10 days of accelerated ageing shows that it induced localized corrosion, possibly where the coating was thinner.